Tube rectifiers, 5V vs 6.3V?

[Flundran]

Is there any advantage using a 5V rectifier, like the 5Y3 or 5R4 over using a 6,3V rectifier like EZ80 or EZ81? I'm looking to build a vari-mu limiter inspired by the classics like BA-6A and Sta-level. Most models seem to use a 5V rectifier. But it seems easier finding a suitable power transformer for my project if can do without the 5V tap.

 

[RSRecords]

Isn’t there something with isolating the winding between the amplifier heaters and the rectifier windings? I’m way too ignorant on this subject to say for sure but I thought there was something to having the power on a different winding than the audio tubes be it another 6.3 or 5vac

 

[Flundran]

Isn’t there something with isolating the winding between the amplifier heaters and the rectifier windings? I’m way too ignorant on this subject to say for sure but I thought there was something to having the power on a different winding than the audio tubes be it another 6.3 or 5vac

That may be the case, I see many power transformers with multiple 6,3 V windings on the secondary.

 

[emrr]

Use whichever works with your PT....which should have a separate rectifier winding.

 

[merlin]

5V rectifiers usually need a floating heater winding, because their cathode is internally connected to their heater.
6.3V rectifiers usually have an isolated heater so they can share the same heater supply as all the other tubes (they have thicker heater-cathode insulation).
Use whichever you like.

You could just use SS diodes of course, no one will judge you!

 

[Evertide]

All old vari-mu limiters use direct heated cathode...

With a indirect heated cathode you can ground the heater...

 

[Mr. Moscode]

The 5U4 heater IS the cathode. 5U4s were cheap and plentiful in the day. And they are capable of more current than EZ80 or EZ81, and they warm up faster.

 

[rock soderstrom]

Use whichever works with your PT....which should have a separate rectifier winding.

6.3V rectifiers usually have an isolated heater so they can share the same heater supply as all the other tubes (they have thicker heater-cathode insulation).

That may be the case, I see many power transformers with multiple 6,3 V windings on the secondary.

This is an interesting topic. As far as I know, a separate heater winding on the PSU transformer is not required for EZ80/81. On the other hand, I have seen schematics in which exactly these rectifier tubes have nevertheless been given their own heater winding.

So my question is, do I have to reckon with any disadvantages if I have the rectifier tube with a signal tube on the same heater circuit? For example, an EF86 in a microphone headamp and an EZ80 in the corresponding power supply unit?

 

[merlin]

So my question is, do I have to reckon with any disadvantages if I have the rectifier tube with a signal tube on the same heater circuit? For example, an EF86 in a microphone headamp and an EZ80 in the corresponding power supply unit?

With particularly high HT voltage sometime those rectifiers do develop a cathode heater short, even though the datasheet says it is within limit. The 6X4 and 6X5 had bad reputations. Shorts seem to be rare for 'normal' HT voltages, like 250V-300V range, but if the transformer happens to come with a rectifier heater winding it may as well be used, eliminating any possibility of a k-h short.

 

[Cqwet Dbdfte]

Grounding a rectifier heater winding, even if indirectly heated, is asking for trouble. Remember there will always be some internal transformer leaking from HV windings to all others.
Keeping HV separate from others may incur separate transformer or separate shields inside transformer.
Vacuum rectification means more heat inside box, smaller filter caps, more space, compared to silicon, (which can be series'd with power resistors to mimic vacuum rectifier voltage loss.)
Use Silicon carbide diodes for no reverse recovery, and wire wound series resistance for bonus inductance.